We are exactly one week away from a giant change in america's health care system. Mark the date. A milestone for obama care. Tonight the president is bringing out the big gun to argue it will lead to a healthier and cheaper medical cost for americans, even as its critics make one more stand against it. Abc's bob woodruff now. Reporter: Tonight two presidents introduced by a possible future one. Reporter: The more I thought about it the more I realized how much they have in common. Reporter: Call it bill clinton to the rescue. One week before people line up for obama care, the president turns to the man he calls his secretary of explaining stuff. When you have universal enrollment you can manage your costs better and cut your costs down. Inflation and health care dropped for the first time in 50 years. Reporter: For bill and hilary, a family fight. 20 years ago, their push failed, but now in order to fund the changes obama won most of the uninsured must sign on or face a penalty. The most important thing, obviously, is just to get people enrolled in this. Reporter: Today's push comes as republicans are fighting to defund the law. Senator ted cruz today staged a protest speech on the floor of the senate, one that could last until the morning. I intend to speak in opposition. Reporter: It's a losing battle. Children can remain on their parents' insurance until they are 26 and those with pre-existing conditions are guaranteed coverage. First we got to get everybody to sign up. Reporter: Still many americans are not sold. It's unclear what a last minute push from even bill clinton will do to change that. Bob woodruff, abc news, new york.

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